Voltmeter



(No Model.) 2 sheets sheet 1.

M. M. GARVER. VOLTMETER.

No. 425,068. Patented Apr. 8, 1890.

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(NqModeL) 2 Sheets-Sheet 2. M. M. GARVER. VOLTMETBR.

No. 425,068; Patented Apr. 8. 1890.

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MADISON M. GARVER, OF NEIVARK, NEW JERSEY.

' VOLTMETER.

SPECIFICATION forming part of Letters Patent No. 425,068, dated April 8, 1890.

Application filed December 14, 1.889. Serial No. 333 1768. (No model.)

To all whom it may concern:

Be it known that I, MADIsoN M. GARVER, of Newark, Essex county, New Jersey, have invented a new and useful Improvement in Voltmeters, of which the following is a specification.

My invention relates to an apparatus for measuring the electro-motive force of an electric current.

My invention consists in the novel construction of the instrument hereinafter set forth, by means of which I am enabled to bring the coil in an intense magnetic field formed between the unlike poles of two magnets which are supported on a common axis passing through one side of the coil, and thus materially to increase the sensitiveness of the instrument.

My invention further consists 1n certain constructive details, more particularly hereinafter pointed out.

In the accompanying drawings, Figure 1 1s a top view of the instrument. tion on the line Y Y, and Fig. 3 a section on the line X X, of E1 1.

Similar letters and figures of reference 111- dicate like parts.

A is the base, provided with a chamber or recess B for the reception of the coil.

At 0 are two cylindrical standards, upon which rests a flange D of the reel, spool, or bobbin E. ScrewsF pass through said flange and said standards and into the base A, thus securing said parts together. The reel E 1s box-shaped. In its upper side 1t has a circular aperture G, across which extends a sup- H. In said bar is a short tube or sleeve I. In the lower side of said reel there is a bushing J, which receives a screwstep K. Said step may be jeweled to receive the extremity of the vertical arbor L, which extends up through the sleeve I in bar II.

On the'upper side of reel E and opposite flangeD is a flange M, to which 1s bolted a bracket N. This bracket extends upward and over the reel E, and is provided with a threaded nut, which receives the screw 0. The lower extremity of said screw may be jeweled and forms a bearing for the upper end of the arbor L. Extending from the bracketN is an arm P, having its extremity Fig. 2 is asecbent downwardly. To said extremity is attached one end of a coiled spring Q, the other end of said spring being fastened to a fixed collar R 011 the arbor L. Secured to the arborL below the collar R is a light disk S, to which is attached an index-needle T, which extends over the scale-plate U. Said scaleplate U is supported upon abracket V, which is bolted to the flange D of reel E. The disk S is omitted in Fig. 1, the needle being there shown directly secured to the arbor.

The coil W of the instrument is of insulated wire wound around the reel E longitudinally, and having its terminals connected to the binding-posts 1 and 2, as indicated by dotted lines, Fig. 1.

.The arbor L carries two magnets a and b, semicircular in form and having their oppositely-named poles facin The upper magnet a has its polar extremities in close proximity to the upper side of the thin flat coil W. The lower magnet b has its polar extremities exactly opposite the poles of magnet Cl, and in close proximity to the under side of said coil.

The object of the circular aperture G in the reel E will now be apparent. Its purpose is to allow the poles of the magnet 11 to be brought very near to the coil IV, the magnet rotating within the aperture.

The following advantages result from the above-described construction:

First. The magnets a and b may be made in the form of a ring of suitable steel, which may be cut in two diametrically after tempering and before magnetization. In this wayI am enabled to produce magnets closely alike in strength, and so more nicely determine the astatic quality of the apparatus.

Second. By reason of the semicircular form of said magnets I can bring their respective polar extremities of opposite names into close juxtaposition, allowing, in fact, between them only just enough space to permit the upper layer of wires of the coil to pass through without touching the polar faces. I thus produce an intense magnetic field between said poles, which field is intersected by the field due to the current traversing the coil-wires. Thus I augment .the sensitiveness of the instrumen t.

Third. By making the magnets of comparatively heavy steel bars I increase the magnetic effect and render the same more permanent than is the case with the ordinary thin andlight parallel needles of an astatic galvanometer.

Fourth. The mode of suspension of the mag nets is exceedingly delicate and prevents any possible displacement of said magnets laterally. By means of the screw-pivot bearings O and K the arbor L may be raised or lowered, so as to adjust the magnets with reference to the coil.

Fifth. The working parts are simple, few, and easily separated or assembled.

The operation of the instrument is as follows: The current ,to be measured enters at either binding-post 1 or 2, passes through the coil \V, and out at the other binding-post. I11 accordance with well-known laws the magnets a and Z) then tend to place themselves at an angle to the longitudinal direction of the coil, which angle is proportional to the strength of the current; but as acoil of fine wire of high resistance is employed the angle assumed becomes proportional to the difference of potential between the terminals of the coil, and is also modified by the opposition which the spring oifers to the rotary movement of the arbor L. By reason of the form of the spring this opposition is practically constant in all angular positions assumed by the arbor L. It remains simply to calibrate the instrument and to lay off a suitable scale on the plate U, which scale may be graduated to volts or fractions thereof.

By the term polar extremity of the magnet as herein used I mean the end face of the magnet in contradistinction to the surface on either side, or, in other words, that face of the magnet which is at an angle to the longitudinal axis thereof, if the magnet be regarded as straightened out and not parallel to said axis. The advantage of placing the polar extremities of the magnet in proximity to the surface of the conductor is that a Very much more intense field of force is produced by the magnet directly at its polar extremities than at points along its length on either side thereof, and hence, through the reaction of this field of force upon the field of force produced around the conductor by the current, I attain a greater sensitiveness of the needle than would be possible if the needle were arranged with its polar extremity practically at right angles to the surface of the conductor instead of parallel thereto. The distinction between the arrangement of my magnet-needle with its polar extremities facing the surface of the conductor and the arrangement of the ordinary galvanometer-magnet not having its polar faces so placed will be readily apparent on comparing the needle of my device with the needle of any ordinary astatic galvanometer.

1. In an electrical mcasuring-instrument, a coil of wire and a magnet rotar Y on an axis perpendicular to the periphery of said coil, and having its polar extremities in proximity to and facing said periphery.

2. In an electrical measuring-instrument, a coil of wire, an arbor free to turn passing through one side of said coil and free to rotate therein, and a magnet secured to said arbor and having its polar extremities in proximity to and facing the periphery of said coil.

3. In an electrical measuring-instrument, a coil of wire, an arbor free to turn passing through one side of said coil, and free to rot-ate therein, and two magnets secured to said arbor, said magnets being respectively located within and without said coil, and having their unlike poles opposed and their respective polar extremities in proximity to and facing the inner and outer peripheries of said coil.

4. In an electrical measuring-instrument, an arbor free to turn, two magnets secured thereon and having their unlike polar faces parallel and in close proximity, and a coil of wire, the said coil extending through the interval between the polar faces of said magnets and surrounding one of said magnets.

5. In an electrical measuring-instrument, a hollow spool or bobbin having in one side an opening, a coil of wire upon said bobbin and extending across said opening, an arbor free to turn passing through the portion of said coil extending over said opening, and a magnet supported on said arbor and having its polar extremities entering said opening and facing and in close proximity to the periphery of said coil.

6. In an electrical measuring-instrument, a hollow spool or bobbin having in one side an opening, an arbor free to turn passing through said opening, two magnets supported on said arbor, having their unlike polar faces opposed and parallel, and one of said magnets being located within said spool and having its poles entering said opening, and a coil of wire surrounding said spool and extending across said opening and between said magnets.

7. In an electrical measuring-instrument, a hollow spool or bobbin E, having in one side an opening Gr, an arbor L, free to turn, passing through said opening, and having a bearing at one end in the opposite side of said spool and at the other end in a fixed support, and two magnets supported 011 said arbor,

having their unlike polar faces opposed and parallel, one of said magnets being located within said spool and having its poles entering said opening, and a coil of wire surrounding said spool and extending across said opening and between said magnets.

S. In an electrical measuring-instrument, a hollow spool or bobbin E, having in one side an opening G, a bracket N, supported on said spool, arbor L, free to turn, passing through said opening, and having a bearing at one end in the opposite side of said spool and at the other end in said bracket N, an indexneedle secured to said arbor, and two magnets supported on said arbor, having their IOC unlike polar faces opposed and parallel, one of said magnets being located within said spool and having its poles entering said opening, and a coil of wire surrounding said spool and extending across said opening and between said magnets.

9. In an electrical measuring-instrument, a hollow spool or bobbin E, having in one side an opening G, brackets N and V, supported on said spool, arbor L, free to turn, passing through said opening, and having a bearing at one end in the opposite side of said spool and at the other end in said bracket N, an index-needle secured to said arbor, a scaleplate for showing the deflections of said needle, supported on said bracket V, and two magnets supported on said arbor, having their MADISON M. GARVER. Witnesses:

JAMEs S. GREvEs, M. BosoH. 

